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Preheating from 120V

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gnuarm

Model X 100 with 72 amp chargers
So if I am at a friend's house and only have access to a 120V outlet, can the car be preheated before leaving on a cold morning from the 120V outlet? Is that enough heat to do anything useful, or will preheating deplete the battery?

I'm looking at ABRP and it is telling me even starting at 80% charge I need to charge before reaching my destination 184 miles away. Arrival minimum is set to 10% (100 kWh battery with 6% loss). I calculate this as 2.8 miles per kWh, or in the car's terms, 360 kW/mi. That should not be hard even with a bit of heat. It wants me to stop about halfway to charge for 5 minutes, +11%. I'm thinking a warmup of the battery might get be the bit I need to arrive with enough to spare. But I suppose it is no better to warm the battery than it is to charge it. I only get the 80% if it charges all night.

The car is scheduled to arrive at the intermediate charger with 42% remaining. So I expect the car will be conditioning the battery. It's only 85 miles, but an hour 45 minutes driving (the first 30 miles are back roads) and I don't think the battery will be warm on it's own. It will get down to 24°F tonight. Will the 1 kW charging do much for the battery temperature?
 
A 120V 12A "normal" outlet provides 1.44kW of power. Since the computer is running when the car is awake, take out 200-250w from that and you end up with 1.2kW. Conditioning the car does two things: heat the interior and heat the battery. The interior heating can consume up to 6.5kW (PTC) and probably somewhat less than that for heat pump... maybe 3kw? Battery heating takes 6.5kW (dual motor) and around 3-3.5kW (single motor). Clearly, 1.2kW will not be able to keep up. You will lower your SOC. It will be marginally better than not having any input power.

EDIT: Battery heating will eventually stop, and cabin heating will reduce when the cabin reaches temperature... At that point I suspect you'll need the full 1.2kW to keep the cabin warm.
 
Oh, realized you had an additional question at the end. If you let the battery cool down too much, when charging starts all the 1.2kW of energy will be used to warm the battery. It won't start really charging until the battery reaches its target. Might take a long while before taking any charge, but at least during that time you will not lose SOC to heat the battery.
 
You might even run into problems charging at all if you're on 120v and the temperature is low enough. Generally speaking, it's better to charge as much as possible rather than trying to warm the battery. This thread on Reddit was extremely interesting to read. The general takeaway is that when charging, it keeps the battery somewhat warm. When you're driving, the car does a number of clever things to warm things up further. After reading the thread, I would personally try to charge the battery as much as possible, and if it reaches the desired charge limit, I would precondition before leaving.
 
A 120V 12A "normal" outlet provides 1.44kW of power. Since the computer is running when the car is awake, take out 200-250w from that and you end up with 1.2kW. Conditioning the car does two things: heat the interior and heat the battery. The interior heating can consume up to 6.5kW (PTC) and probably somewhat less than that for heat pump... maybe 3kw? Battery heating takes 6.5kW (dual motor) and around 3-3.5kW (single motor). Clearly, 1.2kW will not be able to keep up. You will lower your SOC. It will be marginally better than not having any input power.

EDIT: Battery heating will eventually stop, and cabin heating will reduce when the cabin reaches temperature... At that point I suspect you'll need the full 1.2kW to keep the cabin warm.

So there's no way to warm the battery without heating the cabin??? That's pretty nutz. The cabin takes 10 minutes to warm up enough (seats and steering wheel is all that's needed), but the battery takes a long time, even on a level 2 charger.
 
You might even run into problems charging at all if you're on 120v and the temperature is low enough. Generally speaking, it's better to charge as much as possible rather than trying to warm the battery. This thread on Reddit was extremely interesting to read. The general takeaway is that when charging, it keeps the battery somewhat warm. When you're driving, the car does a number of clever things to warm things up further. After reading the thread, I would personally try to charge the battery as much as possible, and if it reaches the desired charge limit, I would precondition before leaving.

I don't know for sure, but it looks like ABRP will report my battery temperature as "Initial vehicle temperature". I just returned and am headed out again tomorrow with the same itinerary. This reading is now 74°F. The car is charging from 120V for the next six hours. I'm wondering if simply charging at 1 kW will do much to keep the battery warm. The present temp as reported by the Tesla app is 39°F and the forecast low is 38°F.

Today was terrible with the car telling me to stop midway for a 5 minute charge, but actually wanting a 15+ minute charge by the time I stopped. I cut that a bit short and barely made it to the next charger (where I could eat breakfast). It seems when it uses the battery for preheat, that does not get factored in at the beginning, but only after the drain increases, so the 5 minute charge turned into a 15+ minute charge.

People want to make charging sound like a snap, but that's only true if you are not trying to make a schedule. Tonight I won't even get 6 hours of sleep and need to head out again with even less charge than yesterday. To reach the charger I like is 178 miles and I expect to have a charge level of 71% before leaving. At least the battery is starting at a higher temperature. I will also try to keep my breakfast shorter than today. I will take time to charge after visiting the customer this time. It's just that the whole trip is not even 200 miles one way and I have to charge twice in each direction. I guess I could learn to be happy eating breakfast in gas stations and not have to stop at a place that has good food and a charger.
 
I don't live in a cold climate, but I definitely see many users' stories that EVs still have issues in cold weather. I wish you luck in your travels. Hopefully things will go smoother.

From the thread I linked, the charging itself doesn't warm the battery much at all, but when charging, the car will automatically use some of the wall power to warm the battery instead of charging, keeping it above a minimum temperature. The temperature won't let you use the full amount of regen, but the battery should be warm enough to drive off and also warm enough to allow for some regen braking. Basically this means that if you leave things plugged in and charging, you don't need to worry about preconditioning.

For comfort, you can set to precondition before getting in the car, but I don't think it will make much of a difference in overall range. Assuming you haven't reached your charge limit, any energy spent warming the battery rather than going into the battery is just energy that would have been used to warm the battery as you're driving. However, from the thread, it sounds like the car does some clever things to heat the battery using energy that otherwise would be lost, so it might make sense to just let the car keep charging. In either case, I don't think there's a significant difference -- so as long as your charger has been non-stop pumping as much energy into your car as it can (whether to charge or to warm things up), you're getting the most range.
 
I did get an answer from the ABRP forum. They say the Initial vehicle temperature is a made up number to account for a number of factors including the cabin heating. It also includes battery temperature in "ID vehicles" which I assume means Volkswagens. So I guess in the Tesla it does not include the battery temperature (since they are not heated while driving unless a Supercharger is the destination). I've asked if it includes the loss of energy from the temperature change.
 
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